1. Field of the Invention
The present invention relates to a semiconductor light emitting device, and more particularly, to a nitride semiconductor light emitting device that improves light extraction efficiency using a textured structure formed in-situ on a semiconductor layer of a nitride semiconductor structure, and a method of manufacturing the same.
2. Description of the Related Art
A light emitting diode (LED) is a device used for converting electrical energy to infra red rays, visible light, or other light using the characteristics of a compound semiconductor. The transformation of the electrical energy into optical energy can be divided into heat radiation and luminescence. The luminescence includes photoluminescence according to excitation by light, cathode luminescence generated by scanning X-rays or an electron beam, and electroluminescence (EL). Here, the light emitting diode is a kind of EL device, and presently, the most widely used light emitting diodes employ an III-V group compound semiconductor.
The III-V group compound semiconductor is a direct transition semiconductor, and is widely used for the LED or a laser diode (LD) since it provides stable operation at a higher temperature than other semiconductors. The III-V group compound semiconductor is typically formed on a substrate formed of sapphire Al2O3 or SiC. To improve the light emission efficiency, or light extraction efficiency, a variety of LED structures have been studied. One of these is a textured structure on a semiconductor layer on an upper part of an active layer of the LED.
FIGS. 1A and 1B are schematic drawings illustrating light paths at an interface of material layers having different refractive indexes. In FIG. 1A, the material layer has a flat interface, and in FIG. 1B, the material layer has a textured structure interface.
Referring to FIG. 1A, light passing from a first material layer 11 having a greater refractive index into an air layer 12 having a smaller refractive index (n=1) must enter a flat interface 13a at at least a predetermined angle. If the light enters at a smaller angle, the light is totally internally reflected at the flat interface 13a, resulting in the reduction of the light extraction efficiency. To avoid the total internal reflection of light, a method of using a non-flat interface has been attempted.
Referring to FIG. 1B, a non-flat interface, i.e. a textured structure interface 13b, is formed between the first material layer 11 and the air layer 12. Accordingly, the light has an angle of incidence greater than the predetermined angle at the textured structure interface 13b where the light passes from the first material layer 11 into the air layer 12. Thus, the extraction efficiency of light can be improved.
FIG. 2A is a cross-sectional view of a conventional LED having the textured structure as described above. A p-electrode 22, a p-GaN layer 23, an InGaN active layer 24, an n-GaN layer 25, and an n-electrode 26 are sequentially formed on a lower structure 21. Here, the textured structure 27 is formed on the surface of the n-GaN layer 25. The textured structure 27 is formed to control the incidence angle for best extraction of light generated by the active layer 24 into the air layer through the n-GaN layer 25, since GaN has a greater refractive index (n=2.5) than the air layer (n=1). FIG. 2B is a SEM image of the textured structure 27, which is formed of a material such as H3PO4 by wet etching.
However, in the conventional art, to form the textured structure 27, a chemical etching process must be additionally performed after a process for forming a semiconductor LED. Therefore, the manufacturing process is complicated, and productivity is reduced.